﻿using System;

namespace Strive.Core.Services.Poll.Types.TagCloud.Clustering
{
    public class NormalizedLevenshteinDistance : IDistanceAlgorithm<string>
    {
        public const double Threshold = 0.4;

        public double CalculateDistance(string x, string y)
        {
            var maxDistance = Math.Max(x.Length, y.Length);
            return LevenshteinDistance(x, y) / (double) maxDistance;
        }

        /// <summary>
        ///     Compute the distance between two strings.
        /// </summary>
        public static int LevenshteinDistance(string s, string t)
        {
            var n = s.Length;
            var m = t.Length;
            int[,] d = new int[n + 1, m + 1];

            // Step 1
            if (n == 0)
            {
                return m;
            }

            if (m == 0)
            {
                return n;
            }

            // Step 2
            for (var i = 0; i <= n; d[i, 0] = i++)
            {
            }

            for (var j = 0; j <= m; d[0, j] = j++)
            {
            }

            // Step 3
            for (var i = 1; i <= n; i++)
            {
                //Step 4
                for (var j = 1; j <= m; j++)
                {
                    // Step 5
                    var cost = t[j - 1] == s[i - 1] ? 0 : 1;

                    // Step 6
                    d[i, j] = Math.Min(Math.Min(d[i - 1, j] + 1, d[i, j - 1] + 1), d[i - 1, j - 1] + cost);
                }
            }

            // Step 7
            return d[n, m];
        }
    }
}
